Accessibility, a criterion for the choice of visual coding rules / P.A. van der Helm, E.L.J. LeeuwenbergAccessibility and simplicity of visual structures / Peter Arnold van der HelmAccessibility, a criterion for regularity and hierarchy in visual pattern codes / P.A. van der Helm & E.L.J. LeeuwenbergSerial pattern complexity : irregularity+ hierarchy / P.A. van der Helm, R.J. van Lier, & E.L.J. LeeuwenbergAvoiding explosive search in automatic selection of simplest pattern codes / P. van der Helm, E. Leeuwenberg