Give a regular expression for a certain type of scientific notation for real numbers on which the following rules hold. Let sigma = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, "+", "-", e}. The number can be preceded by a "+" or "-" sign or the sign may be absent. Numeric values must be of the form cb_1 b_2 ... b_n where b_i is any digit, but c must be nonzero. The number may be followed by an exponent field of the form e"+" yy or e"-"yy, where y can be any digit