This is probably very basic indeed, but I've just ran into a proof that seems to imply that letting f:X→Y, C⊆X and P⊆Y, Q⊆Y,
f(C)=P∪Q⟺C=f−1(P∪Q),
which I can only understand to be true if f is bijective. Am I having a mental blackout?
Thanks,
Miguel
I have injection f:A→B and I want to get bijection. Can I just resting codomain to f(A)? I know that every function i...
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