简化了条件表达式

Signed-off-by: szdytom <szdytom@qq.com>

sections/1B.typ

@@ -63,19 +63,19 @@
 	令 $infinity$ 和 $-infinity$ 是不在 $RR$ 中的不同对象。以最符合直觉的方式定义 $RR union {infinity, -infinity}$ 上的加法和标量乘法。具体而言，两个实数的和和积照常定义，而对于 $t in RR$，我们定义
 
 	$ t infinity = cases(
-		-infinity wide& "若 " t<0 "，",
-		0 &"若 " t=0 "，",
-		infinity &"若 " t>0 "；")
+		-infinity wide& t < 0,
+		0 & t = 0,
+		infinity & t > 0)
 		wide
 		t (-infinity) = cases(
-			infinity wide& "若 " t<0 "，",
-			0 &"若 " t=0 "，",
-			-infinity &"若 " t>0 "；") $
+			infinity wide& t < 0,
+			0 & t = 0,
+			-infinity &  t > 0) $
 
 	#tab 以及
 
-	$ t + infinity &= infinity + t = infinity + infinity = infinity "，" \
-		t + (-infinity) &= (-infinity) + t = (-infinity) + (-infinity) = -infinity "，" \
+	$ t + infinity &= infinity + t = infinity + infinity = infinity \
+		t + (-infinity) &= (-infinity) + t = (-infinity) + (-infinity) = -infinity \
 		infinity + (-infinity) &= (-infinity) + infinity = 0 $
 
 	#tab 具有这样的加法和标量乘法的 $RR union {infinity,  -infinity}$ 是 $RR$ 上的向量空间吗？解释一下。