Revert "[core] visited as propery"
Revert "[core] visited as propery"

This reverts commit a4ce1d473c13fa5cb577e4ff3dbdf76aa6a1a57f.

ptonner/GPy,jameshensman/GPy,avehtari/GPy,beckdaniel/GPy,avehtari/GPy,ysekky/GPy,befelix/GPy,ysekky/GPy,buntyke/GPy,Dapid/GPy,befelix/GPy,SheffieldML/GPy,dhhjx880713/GPy,mikecroucher/GPy,avehtari/GPy,esiivola/GPYgradients,PredictiveScienceLab/GPy,beckdaniel/GPy,esiivola/GPYgradients,dhhjx880713/GPy,ptonner/GPy,PredictiveScienceLab/GPy,esiivola/GPYgradients,AlexGrig/GPy,PredictiveScienceLab/GPy,beckdaniel/GPy,Dapid/GPy,SheffieldML/GPy,mikecroucher/GPy,ysekky/GPy,buntyke/GPy,jameshensman/GPy,AlexGrig/GPy,mikecroucher/GPy,buntyke/GPy,maaskola/GPy,maaskola/GPy,jameshensman/GPy,ptonner/GPy,SheffieldML/GPy,maaskola/GPy,Dapid/GPy,maaskola/GPy,SheffieldML/GPy,jameshensman/GPy,esiivola/GPYgradients,Dapid/GPy,buntyke/GPy,mikecroucher/GPy,dhhjx880713/GPy,beckdaniel/GPy,dhhjx880713/GPy,befelix/GPy,befelix/GPy,PredictiveScienceLab/GPy,ysekky/GPy,avehtari/GPy,ptonner/GPy,AlexGrig/GPy,AlexGrig/GPy