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# vars returns a list of variables used in the problem
# xvars and yvars only returns x's and y's
xvars = function (object) colnames(object$xRefs)
yvars = function (object) colnames(object$yRefs)
vars = function (object) list(xvars=colnames(object$xRefs),yvars=colnames(object$yRefs))
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