A problem of scheduling partially ordered unit-time tasks processed on dedicated machines is formulated as a mixed graph colouring problem, i. e., an assignment integers (colours) {1, 2, …, t} to the vertices (tasks) V {ν1, ν2, νn}, G = (V, A, E) such that if vp and vq are joined by edge [νp, νq] ∈ E their colours have be different. Further, two νp νq arc (νi, νj) colour vertex νi has no greate...