Remark 1.5.4.2. In the situation of Definition 1.5.4.1, we will often indicate a lifting problem by a commutative diagram
\[ \xymatrix@C =40pt@R=40pt{ A \ar [d]^{f} \ar [r]^-{u} & X \ar [d]^{g} \\ B \ar [r]^-{v} \ar@ {-->}[ur]^{h} & Y, } \]
which includes a dotted arrow representing a hypothetical solution.