这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

				#include "e.h"								void eqnbox(int p1, int p2, int lu)				{					double b, h;					char *sh;					extern char *IRspace;									yyval = p1;					b = max(ebase[p1], ebase[p2]);					eht[yyval] = h = b + max(eht[p1]-ebase[p1], 						eht[p2]-ebase[p2]);					ebase[yyval] = b;					dprintf(".\tS%d 					sh = pad(class[rclass[p1]][lclass[p2]]);					if (lu) {						printf(".nr %d \\w'\\*(%d%s'\n", p1, p1, sh);						printf(".ds %d \\h'|\\n(09u-\\n(%du'\\*(%d\n", p1, p1, p1);					}					printf(".as %d \"%s\\*(%d\n", yyval, sh, p2);					rfont[p1] = rfont[p2];					rclass[p1] = rclass[p2];					sfree(p2);				}