Writing\Proposition\Strictly_implies

The strict implication truth-functor.  Its truth-table is:

Often implication truth-functors are mistakenly interpreted as denoting causality; they should rather be interpreted as indicating correlation.  In this case X and Y must be true or false simultaneously for the whole expression to evaluate as true.  Thus it is possible that X is a necessary cause of Y (or Y of X) but it may not be.  If it is intended to assert that X causes Y this should be claimed explicitly in a declarative statement.