In graph theory, this man lends his name to a closed path that traverses every edge precisely once. The topological formula named for this man states that faces minus edges plus vertices equals two for any polyhedron, giving 
In graph theory, this man lends his name to a closed path that traverses every edge precisely once. The topological formula named for this man states that faces minus edges plus vertices equals two for any polyhedron, giving the surface a value of two for his namesake characteristic. Another equation named for him relates the complex (*) exponential function to cosine of x plus i times sine of x. For 10 points, identify this namesake of a "phi" function, a prolific Swiss mathematician for whom the number e was supposedly named.
In graph theory, this man lends his name to a closed path that traverses every edge precisely once.
Leonhard Euler