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Hello, ( ) I have naive idea and need your confirmation. ( ) That sentence as the target means that the speaker wants the thing known for / unto us that it needs a lot of effort, skill, and it = someone to climb the mountain. Thank you for your help. ( ) Here, "for us" = make the thing known to / for us or make sense of the thing clear for / to us
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Again, what in the world do your parentheses mean?
My board can not display my writen in line by line. That is used for having them clear to see.
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Then please get a new 'board', whatever that might mean.
"The mountain is difficult for us to climb"
bepleasedHere, "for us" = make the thing known to / for us or make sense of the thing clear for / to us
No. You seem to want to take "for us" out of the sentence and apply its meaning to the sentence itself.

"For us" means that climbing the mountain is difficult for us -- it might not be difficult for someone else.
Hi khoff,Thanks a lot.It enlighten me.
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Hi khoff,It extends the influence to more senetnces. (as you say) be difficult that needs more effort, skill and has "us" as its an intended aim; e.g. ( 1 ) Someone are hard to satisfy. (that has "the act of to satisfy them" as its purpose ) ( your words have me get an idea ) Its formation and the way of expression is even with "He is adverse to violence." / " The result I was opposite to what we expected."
Hi khoff,Further, Someone are too hard to satisfy. ("too" has "hard" from against to stopping satisfying )