  A set of lines in $\mathbb{R}^d$ passing through the origin is called
equiangular if any two lines in the set form the same angle. We proved an
alternative version of the three-point semidefinite constraints developed by
Bachoc and Vallentin, and the multi-point semidefinite constraints developed by
Musin for spherical codes. The alternative semidefinite constraints are simpler
when the concerned object is a spherical $s$-distance set. Using the
alternative four-point semidefinite constraints, we found the four-point
semidefinite bound for equiangular lines. This result improves the upper bounds
for infinitely many dimensions $d$ with prescribed angles. As a corollary of
the bound, we proved the uniqueness of the maximum construction of equiangular
lines in $\mathbb{R}^d$ for $7 \leq d \leq 14$ with inner product $\alpha =
1/3$, and for $23 \leq d \leq 64$ with $\alpha = 1/5$.
