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+// This file is part of www.nand2tetris.org
+// and the book "The Elements of Computing Systems"
+// by Nisan and Schocken, MIT Press.
+// File name: projects/08/FunctionCalls/FibonacciElement/Main.vm
+
+// Computes the n'th element of the Fibonacci series, recursively.
+// n is given in argument[0].  Called by the Sys.init function 
+// (part of the Sys.vm file), which also pushes the argument[0] 
+// parameter before this code starts running.
+
+function Main.fibonacci 0
+push argument 0
+push constant 2
+lt                     // checks if n<2
+if-goto IF_TRUE
+goto IF_FALSE
+label IF_TRUE          // if n<2, return n
+push argument 0        
+return
+label IF_FALSE         // if n>=2, returns fib(n-2)+fib(n-1)
+push argument 0
+push constant 2
+sub
+call Main.fibonacci 1  // computes fib(n-2)
+push argument 0
+push constant 1
+sub
+call Main.fibonacci 1  // computes fib(n-1)
+add                    // returns fib(n-1) + fib(n-2)
+return