propositional logic

implement main0 () = print"Hello World!\n"




abstype basicprop (prop)

absprop andprop (prop, prop)

absprop trueprop 

datatype formula (prop) of
| {x:prop} atom (x) of basicprop (x)
| {x1,x2:prop} andopr (x1, x2) of (formula x1, formula x2)
| True (trueprop)