instruction:
Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.
question:
In computer programming, when you append a 'string' to another, you add it to the end of the former string. E.g. String string1 = 'abcd'; String string2 = 'efgh'; Appending the two strings would give 'abcdefgh' But what if I wanted to add string2 before string1 to have the result: 'efghabcd' What would be a good name for that that reverse operation? What is the opposite of 'append'?.
answer:
Prepend: (computing, linguistics, transitive) To attach (an expression, phrase, etc.) to another, as a prefix.

question:
I've been asked to give lectures on electromagnetism in English, but I encounter many problems trying to express mathematical formulas since they are written and I do not know how to read them. Are there any references which elaborate the formulas and express what should we call any mathematical sign?.
answer:
The following references are useful: Pronunciation Guides for Mathematical Notation, Expressions, and Greek Letters (Reference list) Reading Mathematical Expressions (PDF) How can we speak math? (PDF)

question:
You won't catch the train if you don't leave in time You won't catch the train if you won't leave in time I'm pretty sure the correct version is 'You won't catch the train if you don't leave in time', but I'm trying to explain it to someone and I don't know how to explain it. I also don't know how to google it. Can you please help me with a simple explanation or a link that explains it?.
answer:
As implied in the comments, the specific meaning of the two are slightly different (albeit both grammatically correct). It helps to break down the contractions. You will not catch the train if you do not leave on time This phrase is neutral in its blame: not catching the train will happen if you, for whatever reason, do not leave on time. You will not catch the train if you will not leave on time This places blame more directly on addressee: 'will not' implies that the addressee plays a causal role in themselves being late for the train, as if they refuse to leave at the correct time.