Since $f$ is one-to-one, if $f(g(x_1)) = f(g(x_2))$, then $g(x_1) = g(x_2)$. Now, since $g$ is also one-to-one, if $g(x_1) = g(x_2)$, then $x_1 = x_2$. Thus, the composition of two one-to-one functions, $f$ and $g$, is one-to-one.
(b) To express $(f \circ
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