Corrected errors when selecting expressions

MathPad/NSIndexPath+MPAdditions.m

@@ -10,6 +10,11 @@
 
 @implementation NSIndexPath (MPAdditions)
 
+- (NSUInteger)firstIndex
+{
+    return [self indexAtPosition:0];
+}
+
 - (NSUInteger)lastIndex
 {
     return [self indexAtPosition:self.length-1];
@@ -58,7 +63,7 @@
     return [[self indexPathByRemovingLastIndex] indexPathByAddingIndex:lastIndex];
 }
 
-- (NSIndexPath *)indexPathWithLength:(NSUInteger)length
+- (NSIndexPath *)indexPathByRemovingIndexesFrom:(NSUInteger)length
 {
     NSIndexPath *indexPath = [[NSIndexPath alloc] init];
     for (NSUInteger position = 0; position < length; position++) {
@@ -67,6 +72,15 @@
     return indexPath;
 }
 
+- (NSIndexPath *)indexPathByRemovingIndexesTo:(NSUInteger)length
+{
+    NSIndexPath *indexPath = [[NSIndexPath alloc] init];
+    for (NSUInteger position = length; position < self.length; position++) {
+        indexPath = [indexPath indexPathByAddingIndex:[self indexAtPosition:position]];
+    }
+    return indexPath;
+}
+
 - (NSIndexPath *)commonIndexPathWith:(NSIndexPath *)indexPath
 {
     NSIndexPath *commonPath = [[NSIndexPath alloc] init];