Felipe Cucker, Marek Karpinski, Pascal Koiran, Thomas Lickteig, and Kai Werther. On real Turing machines that toss coins. PAC-learning from general examples. On the relative sizes of learnable sets. Moti Frances and Ami Litman.
Optimal mistake bound learning is hard.
Michael Frazier, Sally Goldman, Nina Mishra, and Leonard Pitt. Learning from a consistently ignorant teacher. Boosting a weak learning algorithm by majority. Alan Frieze, Mark Jerrum, and Ravi Kannan. Learning linear transformations.