@@ -13,7 +13,7 @@ types can do a lot of the work for you.
1313> If it looks like a duck and quacks like a duck, it must be a duck.
1414
1515Many things in this tutorial are not really something but they behave
16- like something. For example, we'll learn about many things that behave
16+ like something. For example, we'll learn about many classes that behave
1717like dictionaries. They are not dictionaries, but we can use them just
1818like if they were dictionaries. This programming style is known as
1919** duck-typing** .
@@ -110,6 +110,8 @@ things we can do with sets:
110110{' Nitori' , ' theelous3' , ' go|dfish' , ' RubyPinch' }
111111>> > a ^ b # names in a or b, but not both
112112{' RubyPinch' , ' Nitori' , ' go|dfish' }
113+ >> > a - b # names in a but not in b
114+ {' go|dfish' , ' RubyPinch' }
113115>> >
114116```
115117
@@ -388,7 +390,9 @@ code on Python versions older than 3.5.**
388390
389391** *
390392
391- If you like this tutorial, please [give it a
393+ If you have trouble with this tutorial please [tell me about
394+ it](../ contact- me.md) and I' ll make this tutorial better. If you
395+ like this tutorial, please [give it a
392396star](../ README .md# how-can-i-thank-you-for-writing-and-sharing-this-tutorial).
393397
394398You may use this tutorial freely at your own risk. See
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