Mass-radius relations for the polytropic-quark EOS with realistic SLy4 crust. Selected M(R) relations correspond to γ = 4.5, connected to the SLy4 crust at the baryon densities n₀ indicated on the plot (magenta EOS at n₀ = 0.235 fm⁻³, blue EOS at n₀ = 0.21 fm⁻³, green EOS at n₀ = 0.185 fm⁻³, red EOS at n₀ = 0.16 fm⁻³). In all the selected cases, the quark EOS starts at n₁ = 0.335 fm⁻³, the density jump is λ = 1.7, and α = 1 (Eq. (2)). Regions destabilised by the phase transition are indicated by dotted segments. The black line denotes the SLy4 EOS. The green and blue bands correspond to the mass ranges estimated in the low-spin prior case of GW170817 (Abbott et al. 2017).