introduce and use vindex_defined//1
introduce and use vindex_defined//1

mndrix/swipl-devel,jn7163/swipl-devel,mndrix/swipl-devel,edechter/swipl-devel,edechter/swipl-devel,edechter/swipl-devel,koryonik/swipl-devel,koryonik/swipl-devel,koryonik/swipl-devel,mndrix/swipl-devel,edechter/swipl-devel,jn7163/swipl-devel,koryonik/swipl-devel,jn7163/swipl-devel,mndrix/swipl-devel,edechter/swipl-devel,jn7163/swipl-devel,mndrix/swipl-devel,koryonik/swipl-devel,jn7163/swipl-devel