**** testing true, false, operators:

input is  true
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  false
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not a tautology.

input is  true !
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not a tautology.

input is  false !
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  true true &&
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  true false &&
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not a tautology.

input is  false true &&
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not a tautology.

input is  false false &&
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not a tautology.

input is  true true ||
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  true false ||
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  false true ||
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  false false ||
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not a tautology.

input is  true true =>
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  true false =>
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not a tautology.

input is  false true =>
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  false false =>
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  true true ==
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  true false ==
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not a tautology.

input is  false true ==
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not a tautology.

input is  false false ==
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

**** testing less trivial constant expressions:

input is  true false || true &&
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  false true false || ||
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  false true || true false || &&
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  false true false || &&
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not a tautology.

**** testing error checking:

input is  !
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not well-formed.

input is  true &&
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not well-formed.

input is  true ||
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not well-formed.

input is  true =>
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not well-formed.

input is  true ==
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not well-formed.

input is 
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not well-formed.

input is  true true
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not well-formed.

input is  true true && &&
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not well-formed.

input is  true true !
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not well-formed.

**** testing simple non-constant expressions:

input is  x
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not a tautology.

input is  x x ==
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  x y ==
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not a tautology.

input is  x x ! ||
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  x y && ! x ! y ! || ==
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  x ! y ! z ! || ||
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is not a tautology.

**** testing complex non-constant expressions:

input is  a a ! || b b ! || c c ! || d d ! || && && &&
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.

input is  a a ! || b b ! || c c ! || d d ! || e e ! || f f ! || && && && && &&
Enter the expression to evaluate (multiple lines okay, control-D to end):
Input expression is a tautology.