1. names of students who took some 4 credit course
R0 = select cr = 4 from courses	cno name credit cs110 introduction_to_Computing 4 cs210 computer_Programming 4
R1 = join R0 with grades	stno empno cno sem year grade 1011 019 cs110 fall 91 40 2661 019 cs110 fall 91 80 3566 019 cs110 fall 91 95 5544 019 cs110 fall 91 100 1011 023 cs110 spring 92 75 4022 023 cs110 spring 92 60 1011 019 cs210 fall 92 90 2661 019 cs210 fall 92 70 3566 019 cs210 fall 92 90 5571 019 cs210 spring 93 85 4022 019 cs210 spring 93 70
R2 = join R1 with students	stno empno cno sem year grade name addr city state zip 1011 019 cs110 fall 91 40 edwards_P_David 10 Red Rd newton ma 02159 2661 019 cs110 fall 91 80 mixon_Leatha 100 School St brookline ma 02146 3566 019 cs110 fall 91 95 pierce_Richard 70 Park St. brookline ma 02146 5544 019 cs110 fall 91 100 rawlings_Jerry 15 Pleasant Dr boston ma 02115 1011 023 cs110 spring 92 75 edwards_P_David 10 Red Rd newton ma 02159 4022 023 cs110 spring 92 60 prior_Lorraine 8 Beacon St boston ma 02125 1011 019 cs210 fall 92 90 edwards_P_David 10 Red Rd newton ma 02159 2661 019 cs210 fall 92 70 mixon_Leatha 100 School St brookline ma 02146 3566 019 cs210 fall 92 90 pierce_Richard 70 Park St. brookline ma 02146 5571 019 cs210 spring 93 85 lewis_Jerry 1 Main Rd providence ri 02904 4022 019 cs210 spring 93 70 prior_Lorraine 8 Beacon St boston ma 02125
R3 = project R2 on names	name edwards_P_David mixon_Leatha pierce_Richard rawlings_Jerry edwards_P_David prior_Lorraine edwards_P_David mixon_Leatha pierce_Richard lewis_Jerry prior_Lorraine