Status: IN
The collinearity check in `check-if-it-is-a-straight-line` uses cross-product multiplication `(x-x0)*dy - (y-y0)*dx == 0` rather than slope division, making it correct for vertical lines and exact for integer coordinates without epsilon tolerance.
Source: entries/2026/06/06/check-if-it-is-a-straight-line-solution.md