Basic Properties of Periodic Functions

We use the following convention: x, t, t1, t2, r, a, b are real numbers and F , G are partial functions from R to R. Let F be a partial function from R to R and let t be a real number. We say that t is a period of F if and only if: (Def. 1) t 6= 0 and for every x holds x ∈ domF iff x+t ∈ domF and if x ∈ domF, then F (x) = F (x+ t). Let F be a partial function from R to R. We say that F is periodic if and only if: (Def. 2) There exists t which is a period of F . We now state a number of propositions: