Simplify the following text for a Grade 8 native English-speaking person.
Original: Little is known about Sisley 's relationship with the paintings of J. M. W. Turner and John Constable , which he may possibly have seen in London , although these artists have been suggested as an influence on his development as an Impressionist painter , as have Gustave Courbet and Jean-Baptiste-Camille Corot .
Simplified: No one knows if Sisley 's knew the paintings of J. M. W. Turner and John Constable , which he may have seen in London . These artists have been suggested as an influence on his development as an Impressionist painter , as well as Gustave Courbet and Jean-Baptiste-Camille Corot .