Overview--------This is a simple boolean calculator.  It reads a boolean formula and checkswhether it is valid.  In case '-s' is specified satisfiability is checkedinstead of validity (tautology).Language--------The input format has the following syntax in BNF:( [ ... ] means optional,  { ... } means repeated arbitrary many times)      expr ::= iff   iff ::= implies { '<->' implies }   implies ::= or [ '->' or | '<-' or ]   or ::= and { '|' and }   and ::= not { '&' not }   not ::= basic | '!' not   basic ::= var | '(' expr ')'and 'var' is a string over letters, digits and the following characters:    - _ . [ ] $ @The last character of 'var' should be different from '-'.Armin Biere, Johannes Kepler University,Thu Nov 22 15:47:00 CET 2012