If the original fact were stated as " implies or ", then when saying "consider ," we would have a conflict of terms when substituting. Yet the above logic is still valid to show that if then or or if, instead of letting and , one substitutes for and for (and with , substituting for and for ). This shows that substituting for the terms in a statement isn't always the same as letting the terms from the statement equal the substituted terms. In this situation it's clear that if we substitute an expression into the term of the original equation, the substituted does not refer to the in the statement " implies or ."