Theorem fimass

Description: The image of a class under a function with domain and codomain is a subset of its codomain. (Contributed by Glauco Siliprandi, 17-Aug-2020)

	Ref	Expression
Assertion	fimass	$$⊢F:A⟶B\to F\left[X\right]\subseteq B$$

Proof

Step	Hyp	Ref	Expression
1		imassrn	$$⊢F\left[X\right]\subseteq \mathrm{ran}F$$
2		frn	$$⊢F:A⟶B\to \mathrm{ran}F\subseteq B$$
3	1 2	sstrid	$$⊢F:A⟶B\to F\left[X\right]\subseteq B$$