I encountered this problem while proving
$$A\subset B \implies (f(A)\subset f(B))\ne (A\subset B)$$on Zorich Mathematical Analysis. While A and B are subsets of $X$ and $f:X\to Y$
I encountered this problem while proving
$$A\subset B \implies (f(A)\subset f(B))\ne (A\subset B)$$on Zorich Mathematical Analysis. While A and B are subsets of $X$ and $f:X\to Y$