I would use the word would if I could is one example
Once bitten, twice shy.
Yes, "have" can be used twice in a sentence. For example: "I have been told that I have to complete the assignment by tomorrow."
The word 'just' used twice in a sentence: Twice I left him a message and twice he ignored me. The term 'just twice' used in a sentence: I've only been here just twice before.
There is an equiniox twice a year. There is an equinox in March. There is an equinox in September.
Yes, I can use "his" twice in a sentence: He gave his dog his favorite toy.
There is a mouse over there by the door.
I'veno fluency in that language.
atoms are apart of everything in the world!
I have endeavored the darkest parts of the world.
"I envision a world where violence is not an issue.
It is a fallacy that the world is flat.
The results of World War 2 are irreversible