// quadrangle-midpoints-are-collinear-ex261.ggb 27.7s, 18.3s, 16.5s, 10.1s, 9.1s, 7.22s, 6.55s, 6.17s
// [2*v6^2*v8^2*v9^3*v5-3*v6*v8^3*v9^3*v5+v8^4*v9^3*v5+3*v6*v8^3*v9^2*v5^2-2*v8^4*v9^2*v5^2-4*v6*v8^2*v10*v9^2*v5^2+3*v8^3*v10*v9^2*v5^2+v8^4*v9*v5^3-3*v8^3*v10*v9*v5^3+2*v8^2*v10^2*v9*v5^3-2*v6^3*v8*v9^3*v7+3*v6^2*v8^2*v9^3*v7-v6*v8^3*v9^3*v7-6*v6^2*v8^2*v9^2*v5*v7+4*v6*v8^3*v9^2*v5*v7+2*v6^2*v8*v10*v9^2*v5*v7+3*v6*v8^2*v10*v9^2*v5*v7-3*v8^3*v10*v9^2*v5*v7-3*v6*v8^3*v9*v5^2*v7+3*v6*v8^2*v10*v9*v5^2*v7+4*v8^3*v10*v9*v5^2*v7+2*v6*v8*v10^2*v9*v5^2*v7-6*v8^2*v10^2*v9*v5^2*v7-v8^3*v10*v5^3*v7+3*v8^2*v10^2*v5^3*v7-2*v8*v10^3*v5^3*v7+3*v6^3*v8*v9^2*v7^2-2*v6^2*v8^2*v9^2*v7^2+2*v6^3*v10*v9^2*v7^2-6*v6^2*v8*v10*v9^2*v7^2+3*v6*v8^2*v10*v9^2*v7^2+3*v6^2*v8^2*v9*v5*v7^2+3*v6^2*v8*v10*v9*v5*v7^2-8*v6*v8^2*v10*v9*v5*v7^2-4*v6^2*v10^2*v9*v5*v7^2+3*v6*v8*v10^2*v9*v5*v7^2+3*v8^2*v10^2*v9*v5*v7^2+3*v6*v8^2*v10*v5^2*v7^2-6*v6*v8*v10^2*v5^2*v7^2-2*v8^2*v10^2*v5^2*v7^2+2*v6*v10^3*v5^2*v7^2+3*v8*v10^3*v5^2*v7^2-v6^3*v8*v9*v7^3-3*v6^3*v10*v9*v7^3+4*v6^2*v8*v10*v9*v7^3+3*v6^2*v10^2*v9*v7^3-3*v6*v8*v10^2*v9*v7^3-3*v6^2*v8*v10*v5*v7^3+3*v6^2*v10^2*v5*v7^3+4*v6*v8*v10^2*v5*v7^3-3*v6*v10^3*v5*v7^3-v8*v10^3*v5*v7^3+v6^3*v10*v7^4-2*v6^2*v10^2*v7^4+v6*v10^3*v7^4]
aa:=eliminate([2*v11+-1*v5,2*v12+-1*v6,2*v13+-1*v7+-1*v5,2*v14+-1*v8+-1*v6,2*v15+-1*v9+-1*v7,2*v16+-1*v10+-1*v8,2*v17+-1*v9,2*v18+-1*v10,-1*v19*v14+v20*v13+v19*v10+-1*v13*v10+-1*v20*v9+v14*v9,-1*v19*v16+v20*v15+v19*v6+-1*v15*v6+-1*v20*v5+v16*v5,-1*v21*v16+v22*v15,v21*v18+-1*v22*v17+-1*v21*v8+v17*v8+v22*v7+-1*v18*v7,-1*v23*v12+v24*v11+v23*v8+-1*v11*v8+-1*v24*v7+v12*v7,-1*v23*v14+v24*v13,v25*v24+-1*v26*v23+-1*v25*v10+v23*v10+v26*v9+-1*v24*v9,-1*v25*v22+v26*v21+v25*v6+-1*v21*v6+-1*v26*v5+v22*v5,-1+v32*v25*v20+-1*v32*v26*v19],revlist([v11,v12,v13,v14,v15,v16,v17,v18,v19,v20,v21,v22,v23,v24,v25,v26,v32]))