Let I1,I2,I3 be intervals ⊂R. Suppose f:I1→I2 is a surjective continuous function and g:I2→I3 is a discontinuous function. Must the composition g∘f be discontinuous?
There are some easy counter-examples if f is not assumed to be surjective, e.g. taking f to be a constant function, or in a way that "dodges" the discontinuous point(s) of g.
However if such "dodging" is prohibited, I fail to construct such functions nor find an answer from many similar questions on this site. So I am interested to know whether counter-examples exist? If not, is there a proof? Does it have something to do with intermediate value theorem?
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