Modify wording in lesson 21
Modify wording in lesson 21


Former-commit-id: 4d01782855b273840ed95cd57117cf46ade08957 [formerly 93e031629ea3e278f32e9791cca0d4fa64063cf8]
Former-commit-id: d60dc7cc72032b1abd32d55836afa70e9ea327c1
darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide,darkbuck/Halide