Please capitalize where necessary: one of lesniewski's first projects had been to attempt to disprove this principle, but lukasiewicz had published an appendix to his 1910 publication on the principle of contraction in aristotle which caused lesniewski to change to direction of his research.
One of Lesniewski's first projects had been to attempt to disprove this principle, but Lukasiewicz had published an appendix to his 1910 publication On the principle of contraction in Aristotle which caused Lesniewski to change to direction of his research.