Draw the pyramid EFGHS${}_{15}$ in Figure 1. The lateral face $\mathrm { EFS } _ { 15 }$ and the base EFGH of this pyramid form an angle. Justify without further calculation that the measure of this angle is less than $45 ^ { \circ }$; use the following information for this purpose: For the midpoint $M$ of the square EFGH and the point $N$ with $\vec { N } = \frac { 1 } { 2 } \cdot ( \vec { E } + \vec { F } )$, we have $\overline { M S _ { 15 } } < \overline { M N }$.