CNF_convertor

the input will be convert into CNF so that can used in sementic logic

there are some key words:

'neg' means negative 
'iff' means if and only if 
'imp' means implies
'or'  means union (in logic)
'and' means interception (in logic)

• every basic proposition need to express by "()".
• the "()" should not be in the atom expression.
• "{}" should not be appear in the whole sentence.