05B07 1 08A05; Secondary 05A15 1 20N15 1 39B52 1 Primary 20N05 1 alinear variety 1 alinearity 1 bunch 1 central 1 identity 1 left 1 linear 1 middle linearity 1 parastrophe 1 parastrophic orbit 1 parastrophic symmetry 1 quasigroup 1 right 1 semi-alinear 1 semi-central 1 semi-linear 1 truss 1