Possible Clues:

• Yardstick that’s abandoned right for English mathematician
• In maths, graph theory began with Leonhard ____’s negative resolution of the Bridges of Königsberg problem
• Mathematician who wrote the first theorem of graph theory
• Leonhard of pure mathematics
• Graph theory pioneer
• Prolific Swiss mathematician
• Mathematician taught by Bernoulli
• Bernoulli contemporary
• Regret over being punched by heartless low-life in famous summer
• Mathematician is one who could get greasy in speech?