2.1 Let each of 9 and H denote a system operator that maps a function to a function; let x and y denote functions; and assume that all other variables denote numbers. Fully parenthesize each of the expressions below in order to show the implied grouping of all operations. (a) Hx(t)=12+1; (b) SHy(); (c)(x+y; and (d).2H9y